Bariatric surgery including RYGB is also connected with some medical and nutritional effects or complications. This is not surprising since RYGB "bypasses" virtually the entire ventricle and 100-150 cm of the upper part of the small intestine, so problems with the inclusion of, for example B12, iron, folate, thiamin, fat-soluble vitamins (Vitamin A, D, E and K) copper, zinc and selenium are expected. Therefore, it is recommended that all RYGB operated patients substitute vitamin B12, iron and vitamin D. Despite this many develop various nutritional problems after RYGB, which is sparsely registered in Denmark.